Making Noises

As well as building an instrument I an interested in building the other things necessary to make (semi-)musical noises: an amplifier and a speaker cabinet.

Obviously, as with the bass, there are various places you can start from when building an amplifier or a speaker cabinet. It is hard to draw a definitive line, one side of which lies things you made and the other side of which is things you didn’t make. I am not entirely sure which side of that line kits lie, but I shall be using an amplifier kit in the medium-term at least.

In the short term, I have dismantled an old practice combo amp and I’m repackaging the amplifier part into a smaller box and building a new cabinet around the speaker from it. In the combo amp the amplifier is connected to the speaker with a pair of wires which are soldered at the amplifier end and have tabs at the speaker end. This isn’t a system which works well when the two parts are in separate boxes. Happily Neutrik have designed connectors to address this problem, so I thought I would try them out on this project to see how well they work. Unsurprisingly they are excellent.

It seems to me that there was little point in making a speaker cabinet to the same design as the one I destroyed, or to the same design as another I already have. It was an open-backed combo, and I have another of those; I also have a closed-but-ported combo designed to be used for bass. I therefore decided to build a closed cabinet to get a different sound. I also decided to build it in the shape of a tetrahedron rather than the usual cuboid: partly because I thought it might sound good but mostly because I thought it would look cool. It does look cool. I can’t really confirm how a closed tetrahedron sounds because I haven’t acoustically sealed it yet.

What I can say is that as soon as I had got the speaker out of the open-backed fibreboard combo it came in and screwed it onto a triangle of plywood with a suitable hole instead it immediately sounded dramatically better. Probably if I had just replaced the panel which holds the speaker in the combo with a plywood panel it would have made all the acoustic improvement I could possibly want. It would certainly be easier to do that than to construct a tetrahedron, the main problem in doing which is fixing the panels together: obviously you want to screw fixings inside the cabinet (because it is tidier) but you can’t get any force above the screws to drive them in because the 60º internal angle means another panel is always in your way.

So far I have fixed three sides to each other with hinges mounted inside the tetrahedron. This holds together with adequate rigidity to use it as a semi-open speaker cabinet. I need to work out how to affix the final side: obviously I cannot use internal hinges because I can’t get a screwdriver inside the cabinet while all four sides are fitter. Once all four sides are together I’ll caulk the seams and coat the whole thing, probably with carpet tiles.

Assuming all this eventually results in a reasonable sounding speaker cabinet I will set about making another, larger, tetrahedron to contain a 12″ speaker (the scavenged combo speaker is an 8″ unit) which should sound fairly awesome.

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